Alexander g



. n au 3 Sheets-sheet 1.

. u 11. G. -BBLL.- Apparatus for Signaling and GoinmunimtingmalledPhotopho'n-e.

we Model.) Y

A. G. BELL.- Saints-Sheet}. Apparatus for Signaling andCommunicatingcalle'd .7, IQSO.

. Photophone. No. 235,!99.

Patented De c STATES PAT NT OFFICE.

ALEXANDER e; BELL, F wasnmerom mstrniccr'or COLUMBIA, Asslenon T0AMERICANBELL TELEPHONE comm, 0F BO$TON, mss.

APPAR TUS FOR SIGNALING AND comaUmcmmc, CALLED rno'rornousnSPECIFICATION forming of 'I-etters Patent No. 235,19, dated December-7,1880.

' Appllcatlonflled Augustin. 1880. (Nomodeh) I V To all whom it mayconcern:

Be it known that I, ALEXANDER Gamer:

BELL, of Washington, District of Columbia,

have invented an. Improved Apparatus for Signaling and Communicating,called Photophone,-of whichthe followingdescriptiomin connection withthe accompanying drawings, is a specification. My invention consists ina method of utilizing radiantenergy and of applying it by suitableapparatus to produce audible signals and to produce electric signals.

The rays which proceed from the sun and. -other similar sources, fallingupon various I 5 bodies, produce efl'ects generally perceived by thesenses, as'heat or as color. Besides this; and notably when theyfallupon the substances hereinafter mentioned, the energy which theyare-to conveyprodnces in those bodies achange which the sense of touchor the sense of sight has not been able to take notice of.: This.

changed condition may befitly called a' stateof strainfiand I have beenable to make it manifest in various ways in different substances.

of changes. i Thechangesinthe sensitive bodiesemployed int-he apparatusI shall describezfollow'the falling upon-them'withsuch extreme rapiditythat the two are substantially coincident in time as compared withthetime occupied by' any vibrational movement which can be d tected bythe ear. The extent'ot the change 3 5 at each instant depends uponvariation in the amount of radiant energy expended upon th sensitivebody at that instant, and .isapproximately directly proportionalthereto. The change to a greater or less state of strain thus 0 producedin the sensitive body will therefore correspond with the variations inthe distui'bmg cause both in extent and in rapidity of. suc- 068819118.If, therefore, the energy-of the rays acting on the sensitive bodypasses alternately from a maximumto a minimum-gthat is, errhibits avariation of a vibratioiial character' the changes in the sensitivebody'will be there:

by correspondingly controlled iutheir period' of change, in theirdirection'of change, iu'- 0 their amplitude of total change, and also inthe character of' the changes which take .body from'a less to a greaterstate of strain, and vice versa, can impart a corresponding My discoveryand invention relateto this class changes in the energy of thedisturbing rays while passing from a maximum to a minimum and backagain; or, in other words, the which graphically represents the changesthuscaused in the sensitive body will correspond to the curve whichrepresents the variations in the disturbing rays due to natural causes,or which may be impressed upon them by artificialmeans.

- I have discovered and invented a methodl6o and apparatus forvimpressing any desired variation upon the rays or radiant energy fall-1 ing upon the sensitive body. havealso dis- 1 r covered and inve'ntedamethod and an apparatus by which the changes in the sensitive '65 motionto the air. If the changessucceed each other with suflicien't rapidityand possess sufi ficient amplitude, the vibrational movements therebyimparted to the air become sensible as sound-waves, and 'asound \vilLbeheard which will correspond in pitc'h'to the rapidity A with which thesechangessucceed each other, in loudness to their extent, and in qualityto '7 5 thecharacte'rorvibrationalformofthechanges.

The radiant energy which aflects the sensi- .tive body'may be varied inseveral ways. Its source may be controlled when, as in the case ofalamp,-it islin our reaches Therays which convey theenrgy may becontrolled in their 'pastnige from the source to the sensitive bodyforinstance, a part or the whole may be interio pted by screens opaque tothein,'or the whole may have their energy: diminished more or less bythe interposition of substances which ofler resistance tothe. passagewithout wholly inter. rapt-ing it,-orthey maybe more or lessconcentrated upon or diverted from the sensitive 5 body by lenses,reflectors, or other appropriate means. The" sensitive body maybenormally exposed to the'full-force of, the rays, andthen partially orwholly protected from them. It ay-be normally wholly P mmted from them,

and then partially or wholly exposed to. them, 5

'or it may be normallyfpartially exposed to their influence, and thisexposnre'may th alternately increased ordecreased&.

,. I n the forms ofapparatus which I have devisedthe desired variationsintbc rays em; 1pc

ployed .to 'the sensitive produced in these various ways by means of 1mtion imparted to the appropriate part. of the upon the frequency of thatmotion, for their loudness upon its amplitude, and for their qualityupon .the character thereof. When, therefore, as in certain forms ofapparatus which I have devised, a suflicient motion of the appropriatepart of th e tran smitter is caused by the sound-waves which constitutevocal or other sounds acting-upon a disk capable of vibrating, or itsequivalent, the character of motion thus taken up from the air at thetrans mitting-station causes vibrational changes of a correspondingcharacter in the sensitive body, and thereby vibrational movements of acorre- 2o sponding characterin the airat the receivingstation. Thusasimilar sound to that made or uttered at the transmitting-station isheard at the receiving-station.

The receiving-instrument consists of devices to receive the beam fromthe transmitter and direct it upon the sensitive body, together with thesensitive bodyitself, and, when needed, apparatus connected therewitlrtoproduceairvibrationsor sound-waves. I

An essential part of the receiver is the-body sensitive tothe rays whichfall'upon it, and, the contrivances by which, the disturbance thereinproduced by therays is made sensible.

' There are several bodies whose'electric con" ductivity is'vai'ied bythe rays which fallgnpon them from the sun or other sources. 1 Anyvariation in the amount or in theiutensity of the radiant energy sofallinginpon them changes that conductivityorresistance. My apparatus 4current in acircuit, whichv includes-the sensitive body, and alsoincludes a telephonic re? ceiver, which will thereupon give forthasoundwhosecharacten or quality will corre-v Selenium,.when.in theproper-state, isthebody which I have found most efl'ectiveforthispur- Ihave also found that ot'variOtis substances, 56 hard rubber especially,in thin sheets-say phone diaphragm upto three millimeters-is sosensitive, that when the sun-rays, concentrated by lenses orreflectors,are allowed to fall upon it, and theserays arerapidly-intefr- I rupted, the ear, placed in contact with. or in c 'oseproximity to the hard rubber, will I hear proceeding from it a soundwhose-pitch varies with thefrequency of theinterruptions andcog 6o'respondsito that frequency.

, 1 have obtained-audible results by using as areceiver' disk of hardrubber, as described,-

andpla f figo'ld,sil ver, platinum, aluminum, 1 iron, stee antimony,lead, B'ahbittls; metal,

" awesm u me e those changes give risedepend for their pitch uses thiskind of sensitivene's's to varythe' spond to the character of the saidvariations.

. from the-thickness of an ordinary hand-telem -packing, tinned E-iron,in-{ ern phone-diaphragms' These were formed into plates about the sizeand thickness of the ordinaryhand-telephone diaphragms. Similar resultshave been obtained with plates ofmica, paper, difl'erent kinds of wood,patent-leather, 'ulcanized fiber, celluloid, ivory, sil vered glass, andother substances. v

The receiver may be made in the form of a tube. In this case the light,in the form of a converging pencil, is thrown in at one end, so as toreach a focus near the entering, end, and thence diverging so as tostrike the inside of the tube. The operator listens at the other end.-The tube serves as a resonator, and greatly amplifies the efl'ect ofinterruptions whose frequency corresponds with thenormal pitch of thetube. I have obtained audible results with tubes of soft vulcanizedrubber, of brass, and of soft wood, about one-half inch in diameter'orless.

I now proceed to describe certain forms of apparatus in which I haveembodied my invention.

The apparatus employed consists, essentially, of an instrument whichvaries the amount of radiant energy falling upon the sensitive body,(this part of the apparatus I will call the photophonic transmitter, ofan instrument by whichthevariations produced in the sensitive body aredirectly or indirectly made sensible as sound without the interven-.tion' of electricity,-or as electrical variations which are capable ofproducing sounds or sig-.

nals by means of an electric speaking telephonic'receiver orothersnitable electric signaling-instrumen t, (this part of theapparatus Iwill call a photophonic receiver;) andyof various devices forgiving-the proper direction brdifl'usion to the rays employed. Theseinstrumentsmust be suitably arranged and placed with reference'to eachother.

I'haveispoken of the beam-controlling apparatus as the, photophonictransmitter, and

the sensitive body and parts connected with itasthe photophouicreceiver, and thisjs true if .we consider chiefly the action of "thebeam itself; but, considering that form of apparatus, shown whichemploys electricity as a modi- -fied electric speaking-telephone, we mayproperly call the beam-controller, th'e beam, and i theelectrically-sensitive body. a. variableresistance electricspeaking-telephonetransmitter operating to create electrical undulationsby means of sound-waves, and the receivingtelephone as the receiver.

It the rays are-to pass over any considerabledistanceflhey should, toobtain the best result, he formed-'into'aparallel pencil. in order. toprevent-dispersion and loss of effect. At the point .where they are tobe controlled by the transmitter-they arepreferably concen: trated inorderthat a large amount of energy may bqreadil y fcontrolled there, andthis conccntrafionimayrbo wh lly or partially continamen-they rdauh thesensitive body, or they maybe .thereagain concentrated, use as to exthemost eflicient forins of transmitter by availin g myself of the power ofa reflector to change the direction of the rays by changing theinclination of the whole or of any part of its surface.

Figure 1 is a general diagraphic view of a transmitting and receivingphotophonic apparatus embodying my invention in what I have found tobea, simple and .efl'ective arrangement for the productionpt' a musicalsound or note, and Fig. 2 a'detail'thereof illustrating the interrupteremployed in this instance.

A ray from the sun is caused to take a proper direction in any suitablemanner-in this case by reflecting it. from a plane mirror or heliostat,a, into a condensing apparatus, (shown as .a lens, 1),) which should beaplanatic and achromatic to prevent dispersion,.-and which brings thebeam to a focus, as at 2.

p A suitablescreem-as a solution of alum in a glass cell, a, forexample-to obstruct the passage of obscure heat-rays without obstructingthe passage of light, may be used to protect the apparatus from theeffect of heat when the sunlight is used. I have found with certainforms of receiving-instruments employing [selenium sucha heat-screendoes not to any great extent diminish the 'eiiect produced. The passageof the rays at the point 2 may interrupted or controlled in any suitablefginanneras,.for. instance, by an interrupting wheel or disk, 0, pivotedon an axle, (1, so that the periphery of the said disk lies in the-pathof the rays; and at er near the focus-2 this disk is provided with aseries of openings or} holes, 3, (see Fig. 2,) lyingiu the range of thepencil of rays at or near the focal point2.

As the wheel 0 is rotated the rays, willintermittiugly pass throughtheholes 3, and then, be cutoff by the blank spaces between the I holes,which blanks should-be at least as large as the sectional meant the beamat the point 2 to insure its complete interception- A of alternateimpulses and interruptions will thus be produced, constitutingwhat may"he termedan "intermittent-beam. This beam passeson from the focal point2, and may be directed to any desired point. The rays which diverge fromthe focal point2 are again brought to thevcondition of a parallelpencilby the lens :1, and thence pass to; the receiving-instrumente-shown in this instance as a thin disk or diaphragm, f, of hardrubbcr,'r a ced in a suitable frame or inclosi'ngcase, g,'and which, as,hereinbefore stated,'"will beaifected by the intermittent beam fallingon it; in such manh,) bywhich the sound may ner as to producesound-waves, the rapidity or pitch of which corresponds to the rapidityof interruption of the said beam caused by the disk c. The diaphragm fmay be placed in a suitable sonnd-chamberfurnished with a soundpassageor ear-piece, (shown as a flexible tube,

the ear of a listener.

Acondensiug-instrument (shown as a lens, i) is preferably used to.concentrate the rays and increase their efl'ectin the diaphragm f. Thesaid condenser should beaslarge 'aspossible, as the beam of lightissomewhatdispersed in traversing any considerable distance.

It is obvious that other forms of receivingdisk etlre rapidity ofinterruption of the will be correspondingly varied, and conse-. quentlythe pitch ofthe sound produced at mitter the motion which causes theinterrup- I have devised other forms to be used instead of it, and inwhich the screens employed operate by a lonntbfro or vibratory motiongiven pacity to the apparatus.

Figs. 4, 5, 6,7 aresuch formsof apparatus. '1

and adapted .to-s'lide to and fro. upon the fixed grating. 1n thecondition shown in the drawand partially covers the open slit intheother, and a passage equal to about half. the slit is afforded for thepassage of the rays.

. If the movable grating is moved slightly upward, the s ace allowed forthe rays ,is diminished or e fltirely cut ofll. If it be moved slightlydownward, the spaceisincreased, and

if that motion extends thrdugh a' distance thespace allowed for the raysis doubled, and

.portional to the amplitude'of the motion.-

ual'open slits,- as shown in Fig.4, c'r' they may ing, (silver,forexample,) which'may be scraped ofl inf strips to form-the slits. Ithis kind the mostconvenient. 3

I desired, the opaque portions may bepo ish andthe raysreflected'therefromemployed-to aflect the receiving-instrument, the

the slitsennnpolished portion of "the, other,

he conducted to instruments may be used in couuectionwith thereceiving-station. In this form of transequal only to halfthewidth of.thenarrow slitj Ihave found By varying the velocity of rotation ct the'tionsis continuously inithe same direction,

to the movingpart thereof. By means ofthese- 1 am enabled to give anewpower and ca- Fig. 4 representstwo gratings, kl,"of which one, '10, isfixed, while the other, I, is movable,

ings the opaque portion of one. half overlaps the increase or diminutionwill be di rectly' pro-- 1 Such gratings maybe constructed withiact- 7be made of glass covered with an'bpaque coatmaximum amount beingreflected when the polished. portion of one-grating; is opposite 7 I30so that thptays are reflected from the whole surface otl both, and theminimum elfect is- I when the polished portion t one is behind forms ofscreen. For example, the moving that of the other, and thus renderedinoperaportion, being made as; light as possible, can tivcfor'reflecting. In some instances both be attached, as shown in F1g.- 3,to a tuned impnl tions.

gratings may be made movable, inwhich case reed, j,' whichmay be movedby an electro 5 they should be so arranged that any actuating vmagnet,-either directly as an automattc'clrcuitse would move them inopposite direc; breaker, or' by anelectnc currentcontrolled by any ofthe well-known devices for inter- I rays are wholly intercepted;

In the form of jititerceptcr or beam-conrupting 0r varyingacurrent, oran organ-reed I Holler illustrated in .Figs. 5, 6, 7, a series of may beemployed. In eve'ry. such case the 10 slats, m, of opaque material, arepivoted, asat sound, produced at the receivlng-station will 5, in aframe-workin the path of. the rays, the correspond in pitch and nloudness to the pesaid slats being all oscillated simultaneously, riodot'vibration, nd to the amplitude of vilike'the slats of a window-blind,by a rod, or, br'ation of this transmitting-reed.-

connected with. the actuating vibrator'j, as-

' Fig.8 shows fphotophonic apparatus by r 5 shown in Fig, 6. Therodaisconuected with which articulate .speech'may be transmitted.- I allthe slats on thesame side of their pivoted. I have alreadystated that.the sound at the points, so-that they are all movedparallelreceivingfstatiou-due to the efl'ect producedd. by the rayswhich reachthe .sensitive body but in Fig. 7-th e -alternate slats areconnecte .withthe red 1: on oppositesides of their pivthere placedcorresponds to the characterot' as they are closed. These slats,iu'theirn'or- 'which'jreachit l 'Ihe 'hereinbefOi'e describedtransmitters I ma! position, close. about one-half-the' space,

as shown'in the main, Figs. 6 and.7, (tlie rays have been in endedtocontrol merely the passing in'the directionof thearrow,) and by pitch.and the loudness of a simple musical 2 5 their movement in onedirectioutheyincrease note',-.-and the vices in them have thereforetheopen space for'therays to until they. beenadapted merely control theperiod arrive'at the position shown at 6,;where the during whichft e.energy of the beam passes. maximum amount is allowed'ttrpass, while a.:from, its maxim. m "to its minimum, and the movement in the otl'ler'direction decreases the. reagent its'chanfie or the'difi'erence ofenergy 0 amount until, in the position shown tit-7, the betweenits-maximum and minimum;

It will seen that when-theslatsare open, sound having a'complexcharacter'or qualas .shown at.6, they only presenttheiredges.ity, ittis further necessary, first, v,that-the asobstructionto therays, and their thickness props 3 5 may be much less than the open spacebetween chanfi I arfacter shall be impressed upon the them, so thatagreater amountot' rays may be in tts-irays, and upon the motion whichproallowed to pass than when the gratings's hown 'duces themwhilepassing-from one extreme I in Figs. 3 and 4 are used, astheyueverailowto tbeether; and, second, that the voice of the more than half the beam.to pass. --By connectspeakeror the sounds tobe transmitted'shall of 40'ing the rods a nearer the pivots fij the same themselves operate'thephotopho'nic transmit- 5 2o ots, so that they incline-inoppositedirecti'ons the ehanges in the energy of the pencil of rays Inorder to transmit articulate speech, orany rob in the receiver, upon thevariations extent of movement in their rods will giveater'andt'impresstheir own character orform of greater. angular movement to the slats.

-' vibration upon the movable 'part. of the appa- It will be seen thatnone of-these forms .ratus which controls thefbeam.

.- screens or interruptions will give an intermit I'n'the apparatus,Fig.8,.tjhe movable part i r to" tent beam, asherein described, unlessthey of Moreen-grating, la 1, like that shown in Fig. I are whollyclosedat each vibration but 'if 4, isattached'to the center ofa diaphragm, b,there be any vibration at all, the strength, and constructed, mounted,and arranged'in'a soundl consequently the eifect,of the %ucil ofraysc'hamberg'as is usualin electric speaking-tale.

I which pass beyondthe instr ent, though phonetransmittcrs. -W henspoken to, this dianever wholly interrupted, will vary inaccordphragmand. the movable part of the screen ance with of thevibrational movement of the moving the peculiar character of vibrationdue to the part of the transmitter. v fllhese variations quality'of thesound uttered.'- The same char- 1n the strength 1 of the total beam,fallingv acterot' vibrationalchangeis therebyimparted upon the sensitivebody employed in the to the pencilof rays which passes through thereceiver, will cause in its condition-changes instrument, and by them tothe sensitive body which, ll] tgelrrapidity of succession and "in thereceiving-instrument, where'it is made I in their exte t, willcorrespond to the vibrasensible by a sound of corresponding quality,

tionaljmoyement in the transmitter. When and the words uttered into thetransmitter are these changes are made sensible-as -;sound% heard toproceed from the receiver.

the pitchof that sound'and the-loudness o It isobvious that thediaphragm, instead of I that sound will becontrolled- 'by the periodingzoperated directly by the sound-waves, and theamphtude of the motiongiven to the could. be made to vibrate by electrical means,

vibratioualpart of the transmitter...

such as *used .for imparting vibration to the Therearemanyways in whichvibratory mo diaphragm ot a receiving-telephone.

tion can becommunicated to these or' other the period and withtheamplitudeattached thereto take up from the sound-waves IJtiswoll-known that the extent of motion which can given by the voice toa dia- I through line slits, however, some difliculties arise inthe'natureof interference. I have other cases described.

obviated these by another form ,of articulatespeech'transmitter, which Iwill presently describe. i a r In Fig. 8 the radiant body is-s'howli asthe flame ofa candle, p, and: the lens brings the divergentrays thereofto the condition of a parallel beam, which is controlled by the gratingsk l. V Another method isto bring the'rays to a focus, 2, Fig. 9, andinstead of the grating klemploy two plates, is 1', one fixed andtheother connected to the vibrator or diaphragm o, the said plates having ahole, 8, of .the size and form of the image at the focalpoint, and thehole of the fixed grating coincidingwiths aid' image in position toallow all the rays'to pass 7 through it. The movable plate, in passingto and from 'a position with "its holercoinciding' with that of thefixed plate, allows or obstructs the passage of-a greater or lessportion of the pencilof rays, which then directed to andact upon thereceiving instrument, as in the A single plate constructed in thismanner,

1 when properly guided,-will operate in the same 1 vway, and by givingsuch a plate a movement parallel to the axis of the pencil of rays itwill intercept an increasing portion thereof as it "moves from the focalpoint, and, thus control the beam. Y Y

The receiver-, which is shown giu -Fig. 8, de-

pends upon the property hereinbet'ore referred to as belonging tosubstances, notably properly-prepared selenium, of undergoinga great,instantaneous, and substantially proportional increase oficonductivitywhen acted upon by the rays proceeding'f 'oln-the sun and othersimilar-sources.

.-A piece of selenium, S, brought into a suit I able condition andsuitably mounted, forms part of an electric circuit, supplied with acurrent by a-c'onstant electro-motive force, as by thebattery B. ,Thisselenium-is exposed to the rays'which proceed from the transmitter,

I and'every variation causedin its conductilr ity produces a'corresponding variation in the strength of the current. These variationswill,

' 'in' the manner now'well known to electricians,

operate anelectric speaking-telephouereceiver,

T, (or othersensitiv e electricah instrumental placed in thecircujt orconnected with it, and

this telephonic reoeiyerwill giye forth the articulate words whichhavelbeen uttered into i the photophonic transmitter.

i In another application I have described the Q manner nium, j

I now remark, however, that as the selenium, even when in its mostfavorable condition, is of high resistance, it is desirable to interposeit in the circuit in the form of a conductor of but slight length and oflarge area, which may be done very advantageously by some novel ofpreparing and mounting the seleforms of cells to beherein'afterdescribed;

.Some of the best forms of apparatus for this purpose consist;generically, oftwoor more plates of good conducting metal, separated Iby a thin sheet of insulating material placed between each pair ofplates.- This insulating sheet has a-slightly smaller surface than theconducting-plates, and the space thus left is filled up with selenium, which thus serves as a conductor between the two plates. It is obviousthat this 'constructinuenables the selenium to be usedin the shape ofa'conductor of large area, nearly all. of; which is exposed to the rays,and of an extremely short ,which may conveniently be'a sheet of mica,

7 length, equal totherthickness of the insulator; g

while it uses very little selenium, and it is V by heating the metalcell and fusin g the. sole nium into the cavity left betweeuithe twoplates when the insulator is placed between them. A considerable numberof these" cells may be built up side by side and connected in parallel;branch circuits. Besides mica, the.-

paintswhich are employed in- 'paintiug on china may be used to separatethe metal very easy to work the selenium into this shape plates whenbaked. Asthe plates are heated the said paint becomes porcelain. Yariousforms" of cell constructed onthis plan will be are;described 'inotherapplicationsfiled by I myself, and other applications filed by myselfind Mr. Sumner. Tainter jointly, and others V I no ,uuder control-ofnium resistance therein, and the solefiled by Mr. Sumner Tainter, 1 4

The electric circuit being the: V nium nder control of the pencil ofrays, and

the rays under the control of the transmittr 5 ting-instruments, itisobvious that any instru-v men'ts whichfoanbe controlledby slightvariations in an electric current-such asffor iustance, the us'ualtelephonic, instruments-if placed in theielectric circuit with thelsaidselenium,, will'be controlled by and wilLemit' sounds corresponding totheiactiou-of'theflsaid' 1o 5 hereinafter described. Other forms ofcellsI transmitting apparatus oathe beam which falls on the selenium,"

andithis movement, in turn, impresses avibrar36 j 1 Fig. 10 illustratesanother apparatus for; i transmitting 'complex. sounds (or articulatespeech. As, in the form last'described, the

sound-waves due to the voice serve to give to l the movable'p'art-of thetransmittera vibra', tional movement of corresponding; character,

ins

falling upon the sensitive part of the receiver.

-The pencil of rays is passed through a suitableconce'ntratingapparatus, 0., (shown here as a lens,) and alsothrough a heat-absorbingapparatus, a', which prevents the heat-rays from warping the reflectorof the transmitter.

- 1; then falls'upon a reflector, 1', (shown as a plane reflector placedat such an angle as to direct the rays to the receiver 6.) Afterleaving.

' this reflector the rays may be caused to'pass through a lens, (2, inorder to give them the dc sired parallelism, it they do not already pusconcentrated on the reflector than in their, path from the transmitterto the receiver. Arrived there they are caused to fall upon the mirrors.Tracing the path of a single ray from sees it. In the drawings they areshownm'ore sensitive receiver either directly, or, as in the drawings,after. further concentration by'the the lens a andcell aflit will heseen'that its path from the reflector r will depend upon the 7 If the.reflector be so placed normally the.

angle at which-that'portion of the reflector r on which it falls ispresented to it.

the ray will pursue the path toward there-I ceivershown in the drawings,then a slight change in the angle of incidence of that particular rn ywill, ifin one direct-iomso alter the subsequent pat-hpf the-rayas todivertitfrom the receiver, or. if in theother direction will I directupon the receiver, rays which otherwise ought not have reached it. Anysuch change will therefore vary theamouut of radiant en- 'ergy exertedupon the receiver. 1 construct this reflector 1' of some m aterial--suchas glass,

1 silvered, or thin polished metal'which will ta kje' up from thesound-waves of the air their with them as truly as the -diaphragm ot" apeculiar motion and vibrate in accordance speaking-telephone does. As itvibrates, each portion of it departs from its normal position as'part ofa Plane surface, and'bends or tips mo re-or less in one direction or theother. Consequently each y ray' retlected from it is more or lessdiverted from its normal'path,

and thereby the total ain'ount of radiant'cnerg'y exerted 'on'lhesensi'tive receiver by all the raysrefleeted from the transmittervaries at each lns'tant.

The extent of variation from instant to in- .stant,'the direction of thevariation, the period of each variation, and the character of eachvariation depend upon the vibrational movement of thetransmittingirefiectonwhich causes the changes, an (1' therefore thesame character Qf vibrational movement given to the transmitter by thevoice reappears in the variatrons in the radiant energy operative uponthe sensitive part of the receiver, and consequently in-thesouud orother effects due to the changes lll that sensitive body. The wordsspoken against the transmitterare thereupon heard to proceed from. thereceiver. I havefthus transmitted articulate speech, using as areliector a disk of 'silyered glass thirty inches obtained clearer andbetter articulation by using as reflector a disk of thin glass, such asis used for mounting objects for the microscope, properly silvered,andabout two inches yin diameter. 7 n In the drawings the reflector 'r isshown as mounted in a mouth-piece such as is commonly used in telephonesIt is essential that the mouth-piece should beso fixed and the reflectorso-held in it that its normal position should always be the'same,-iuorder that the rays may be directed to the receiver.

it will sometimes be desirable to mount the transmitter so as to give ita universal move- ,ment. A mounting similar to that of a telescope of asurveyofistransit accomplishes this, and a similar graduated limb isoften useful. The mouth-piece or sound-passage may be readily used withthe mirror r in any desired angular position. i

ll do not herein specifically claim this particular form of transmitter,as it is ajoint in- .vention of myself andniyassistant, Mr. SumnerTainter, and will form the subject of a joint. application. V

Asmall telescope attached to the instrunientmay be used as a finder. ihebeam, after passing from the controlling or transmitting apparatus, isreceived, as 'in the other forms; described, upon a collecting andcondensinginstrument, (shown 'in this instance as a parabolic mirror,s,)by which the rays are concentrated on a selenium cell, S, of peculiarconstruction, as will he hereinafter described. The said cell is placedat the focal point of the saidmirror s, and is adjusted in position asshown. It is supported at the end 'of the tube t], passing through asocket at the "sition therein by a set-screw,-u. The electrodes 1112pass out through the said tube, and may be connected with a batteryand telephonic or electrical instruments, as before described'incorinection with Fig. 8.

small telescope or fihderfw, may be employed to enable the operator togive the proper directi'onto the axis of the mirror; or this may be-doneby sighting through the tube t.

in plan and section, Figsll and 12. and the different parts thereof inFig. 13; This cell has an arrangement similar to but in constructionis'difl'erent from, what is known as Siemens spiral. v

T-wo ribbons, a b, ofsuitable conducting material, preferably brass,form the terminals of the poles of the battery B, the said ribbonsinsulating material, which is slightly narrower than the metal strip, soto leave a slight in diameter, of tolerable thickness, and have.

made as aflexible tub'efto enable it to be A simple form of seleniumcell S is shown I being separated, by thin strips 0 of suitable! vertexof the mirror, and held in adjusted polIO pus

open space between the edges of said strips. The whole is then coiledinto a flat spiral, in order to give it a more convenient form forexposure to the action of the rays, a second strip, d ofinsulating-material being inter- "posed to prevent conductive contactbetween between them, as shown at 0 -metal'may be electro-d'eposited onthe edges of the strips to give them the proper salience, or toform-suitable channels for the reception of the selenium.

Another form 'of selenium cell that I have used is illustrated in planand section in Figs.

14, 15. In this case the conducting'and insulating materials arearranged inalternate parallel strips a b 0 -11 and only the alternatestrips 0 of insulating material have a smaller extent .of surface thanthe inclosing metal strips, so that the selenium e, deposited, as beforedescribed, in the channels left for it, will connectonly alternate pairsof the said stripsthat is, connecteach strip 11 with the strip a on oneside thereof, but not with the strip a. on its other side. The strips a5all project on one side and are electrically connected toe gether by therod f and the strips b are connected on the other. side by the rod g,and

each connected set of strips withflone pole of the battery, or, in otherwords, placed in a circuit which islcompleted by the selenium e.

, Another term of cell usedbyuie", and shown in plan and section inFigs. 16, 17, consists, essentially, of a metal box, a, and a disk, b,

fitted in and insulated from it. The said disk is provided with a seriesof tapering holes, 20, and the bottom of the box with a series of pins,

21 of slightly smaller diameter than. the holes,

a .so that when in place the said pins pass into the said holes,leavinga narrow annularspace around each pin. 7 These annular spaces.are filled with meltedselenium e, which thus closes the circuit betweenthe box and disk. 1 do not specifically claim this particular form oicell, as it was invented by my assistant, Mr. Sumner Tainter, by whom anapplication for Letters Patent on the said cell will be filed, in

which i ts construction will be fully described.

Another cell which has been used with excellent results is shown at S inFig. 10, and in side and end views, on a larger scale, in Figs. 18 and19, and in detail in Figs. 20, 2 l 23, 24. Itisnot herein specificallyclaimed, as it will form the subject of a joint application bymyselt'and Mr. Sumner Tainter before mentioned. ,similar to that of thecell described in conihe principle of construction is.

nection with Fig. 14; but the shrfacetobeex posed is cylindrical insteadof plane, such form being preferable when used in connection with aparabolic mirror as the instrument for condensing the rays, as shown inFig. 10.

,Instead of rectangular strips of conducting and-insulating material,circular disks a'. b c are used. Those marked c,of insulating material,are slightly smaller in diameter than'those a. D of conducting material,so that annular channels are left between the edges of the conducting-disks a b, around the periphery of the insulating-disks c and inthis instance such channels are left between all the said disks n. b,

' so that each disk a will be connected by the adjacent annular rings c,of selenium, with'bo'th the disks on either side.

The disks are each provided with a central .hole, .5, to enable them tobe held in proper position on a mandrel, wherethey are clamped betweentwo suitable end plates, 715i, the disks of metal and insulatingmaterial being alternated on the said mandrel. The conducting-disks areelectrically connected togetherin two sets of alternate plates, a 1),between which the circuit is completed by the annular rings of selenium.6, following the channels aroundthe disks of insulating material 0".This connection is accomplished as follows: The disks are provided withholes, shown as four in number. In the conducting-disks two of theholes, 30 31, are

of larger diameter than the other two, 32 33, which are of the same sizeas all four of the holes in the insulating-disks. In placing the .diskson the mandrel the holes are all placed with their centers in line, andthe large holes 30 31 of each conducting-disk are in line with the smallholes 32 33 of the-conducting-disks on each side of it, or, in otherwords,- in a given line of holes all those of the plates a will be ofdifferent diameter from those of the plates b.

A cylinder of conducting material of a diameter-equal to that of thesmall holes driven through a line. of holes will touch and electricallyconnect the alternate conducting-plates having theirsmall holes in thatline, and will not touch theo'th'er plates. 7 Two of the cylinders, fwill connect together all the disksot' one set, as afi'whichiwill formone terminal of the circuit, and the other two cylinders, g ,'willconnect the disks'of the other set, b, which will form the-otherterminal; but the two sets b r w ill be connected by the selenium e.

In order to insure a more perfect connection between the plates a andcylinders f, and the plates b and cylinders g, the said cylinders aremade tubular and one or more slots, 40, cut longitudinally through theirsides. .Wash' ers c, of insulating material, are placed within the largeholes 30 31 in the conducting-disks, so that the said washers completelyinsulate and separate that portion of the disks from the cylinders.

Melted conducting material-as, for example, type-metal-is poured intothe tubes f g, and, passing through the longitudinal slots,

its

dicated by the letter j, but is prevented by -the washers from making acontact with the plates having the large holes adjacent to it, as shownin Fig. 22.

Insteadof the washers c of insulatingma terial, smaller washers or ringsof any material--as, for instance, metal-may be used to confine themolten metal and prevent its contact with the plates at the large holes,the said rings themselves being too small in diameter to touch thesaiddisks.

Instead of using molten metal in the tube to form the connection,pulverized conducting material may be used--as, for example, metalfilings, spelter forming an excellent connector-and in such casethe cellis; much more readily taken apart. Nuts h on the ends of the tubes f gserve to hold the whole together.' The cell is heated and the seleniummelted thereon, and in all cases I have obtained bet ter results byfiling oif the'selenium which covered the edges of the conducting disksor strips, and leaving only the selenium between the said conductingstrips or disks.

After the surface is finishedthe mandrel, if

and a'handle or tube, t, may be screwed into one of the end plates, M,as a means for holdint, the cell in position.

' I have shown an alum cell placed in the path of'the pencil, so thatthe only rays which operated the instrument were luminous rays.

I have also produced audible eflects with a selenium -cell receiver whenI removed the alum cell and substituted a thin sheet of hard rubber -sayone-eighth of an inch thick, and therefore sensibly opaque tolight-andalso when I placed in the path of the rays both the rubber and the alumcell. I do not therefore intend to limit myself to the employment of anyparticular portion of the rays which proceed from the sun or othersimilar bodies.

I have called the apparatus a photophone because an ordinarybeam oflight contains I rays which are practically operative.

I will remark, however, that cutting oft the luminous rays of thesunwhich have passed through the lenses, as by a solution of iodine in bi-I have also employed with the selenium cell the rays of gas, of apetroleum-lam p, and of a,

candle, and of the lime-light. For many pur poses an artificial sourceof light theposi v tion of which can be adjusted at pleasure, andkeptunchanged and uuafi'ected by night or weather, is more convenient thansunlight.

I bane employed prepared selenium as a type of one class of sensitivebodies whose changed conditionmanitested by the variation in theresistance they afiordto a constant cuit of which it forms part,.othersto vary the electro-motive force of current in thecircuit.

The strength of the electric current in the receivingcircuit may also bevaried by varyin g the electro-motive force developed in that circuit.Thus, for instance, a thermopile, when used as the sensitivepart of thereceiver, would also be directly afi'ected by heat-rays, and would giverise to varying currents in a circuit in which it was placed; but inorder that tones may be so produced, the thermopile must be not merelysensitive but much more rapid in its action than those ordinarily known.

Rays ,of light, as distinguished from rays of heat, will develop anelectric current when falling upon the junction of two different metalswhen reduced to the form of thin films. 'Light.falli ng onsensitiveselenium will'also develop a current capable of giving electric signals.In both these contrivances, however, special rapidity of action as wellas great sensitiveness is required.

A beam of heat-rays, by falling upon a ma-' 'teriai arranged to absorbthem quickly and again cool quickly-as fine wires strainedmay be made toexhibit its variations.

The amount of rays allowed to act on thereceivermay be modified bycontrolling the source from which they are derived, instead ofintercepting er deviating them in their path. The well-known manometricflame apparatus is suitable for this purpose. The motion required tooperate such a flame. apparatus may be given, as is well known, by thevoice.

'The supply of gas fora burner may be allowed to pass throughagratingsimilar to that shown in Fig. 4, and when the movable part isvibrated the supply of gas will be controlled accordingly.

The beam may pass from the transmitting to the receiving instrument byother than direct paths, if necessary, and for this suitable reflectorsor other directing-instrument may be employed;

The instruments may be arranged with reference to each other accordingto the uses desired to be made of them. The transmitter and thesensitive body may be placed near together or be separated by anydistance over which the rays can pass efiectively.

.If the transmitter be operated by an electric current, the circuitwhich carries that current may be of any desired length and ar ranged inany appropriateway known to elec- Jtricians.

If an electrically-sensitive receiver be usedas, for example, a seleniumcell-the circuit which contains it-may be extended to any suitabledistance, or' may be connected with another circuit by iuduction ooilsin a'm'aiin'er current, and'a diskot' hardfrnbber as 'atype a'ndforpurposes well known to electricians,

and to those who are familiar with variable resistance electricspeaking-telephones.

Inasmuch as the" rays have no inertia and are inflexible, a slightmotion .of a reflector such, for example, as it will receiveif attachedtothe diaphragm of a receiving-telephonacan notonly be made to manifestitself as ligh t, (as in a reflecting-'galvanometian) but also as sound,or as a variation of an electric current in asecondary'or local circuitsupplied with its own battery. 4

The sound produced in the receiving-telephone is a functionwhich is'afi'ected by at least three variables-namely, the character of thedisturbing rays '01 of their source, the

character of the variation'jn the path of those rays, the character ofthe sensitive body.

In the apparatus shown in the drawings, when mounted for use as therearranged, the second element is all that varies, and the othersremainconstant. In one formwhich I have mentioned that in which thesource. ofrays is a man ometric flame-the variation is in the source itself, thepath of the rays remaining unchanged; but it is obvious that when oneelement is removed and'replaced by a differentone-e. 9., when onesensitive body is replaced by another, one source of radiant energy byanother, one partially-intercepting body by another, the other elementsremain ing the same-this change will produce a corresponding change inthe audible results and can be detected by the sense of hearing.

. I claim- 1. The herein-described method of signaling or communicating,which consists in controlling a beam of rays, as to its'amount or activestrength in accordance with the signals to be given, and receiving thesaid rays on a sensitive substance forminga part of an electric circuitand afi'ected as to :its resistance in accordance with the amount-orstrength of the vbeam received upon it, whereby electric apparatus inthe said circuit ma be controlled to give signals corresponding to thecontrolling influence imparted to the beam.

2. That improvement in the art or method of transmitting or' reproducingsound which consists in giving a beam of rays an undulating orintermittent character in accordance with the sound-waves it is desiredto produce,

and roviding a receivin apparatus adapted P v g a when acted upon by thesaid rays, to produce air-vibrations or sound-waves corresponding to theundulationsor variations in the said of a 'photophonic transmitter, ofmechanism beam, substantially as described. v

3. The herein-describedmethod of transmitting articulate and other soundby caus-' in g, in therays proceeding froma photophonic"transmitting-instrument to a photophonic receiver, undulatory variationsin radianteuergy similar in form to tbs sound-waves accompa radiantenergy to rays whose efiective energy,

exercised upon said sensitive body, is caused to vary in accordance withthe vibrational form of the sound-waves appropriate to the sound to beproduced.

5. The herein-described method of transmitting articulate and othersounds by caus- 'ing the sound-waves which constitute said sounds toproduce similar variations in the beam of rays proceeding from aphotophonic transmitter to a photophonic receiver.

6. In an apparatus for communicating signals, a beam-controllingapparatus to impart a varying character to a beam of rays (from aradiant body) and a receiving apparatus sensitive to the said beam andoperated thereby, to give signals corresponding to the variations in thesaid beam. imparted by the. cona trolling apparatus.

. 7. The herein-describedapparatus for transmittipg articulate and othersounds by causin'g,-in rays proceeding 'from a photophonic transmitterto a photophonic receiver, undulatory variations in radiantenergysimilar in form to the sound-waves accompanying said articulateand other sounds.

8. In combination with a photophonic receiver, a photophonictransmitter,'the source of radiant energy of which is varied orcontrolled substantially as described.

9. In an apparatus for producing or reproducin g sound at a distantstation by meansof variations in radiant energy, means, as described,for varying theamount of snclr energy which reaches the distant stationby motion imparted to the transmitting apparatus.

10. A photophonic receiver adapted to produce, by the action of a beamof varying character from'a radiant source, dynamic or electric efiectscorresponding with said character, substantially as described.

11. In an apparatus for sound-transmission, a device for controllingthebeam during its passage from its source, in contradistinction tocontrolling the source itself, said device being actuated by the waveswhich constitute .said sound to give the beam an undulatory character orvariations in effective stre'ngth similar in form to the saidsound-waves, substantially as described.

l2. In aphotophonic transmitter, the combination 'of a movable and animmovable portion to control the amount of radiant energy passing fromit, substantially as described.

, 13. The combination, with the movable part operating electrically forgiving motion to said part, substantially as described. Y

14. The method of producing a beam of varying character for photoph-mictransmission 1 by con-trolling the amount of radiant energy which isallowed to pass in the desired direction from a constant source.

' 15. A beam-controlling device comprising a vibratory medium and means,as indicated, for varying the amount or radiant enemy ICC which isallowed to proceed from a constant source in a given direction inaccordance with the vibrations of said medium, substantially asdescribed.

16. The combination, with a transmitting apparatus to give a beam fromaradiant bod y an undulatory character or variations in efl'cctivestrength, of a receiving apparatus sensitive to, the said beam andhaving the propcrty of emitting sound under the influence andcorresponding to the character of the said beam, substantially asdescribed.' e

17. In an apparatus for sound-transmission, a transmitting apparatus to'control a beam 0 from a radiant body, and a receiving apparatuscontaining, as a portion oi an electric circuit, a device the electricalcondition of w hich is varied in accordance with the strength orcharacter of the beam afiecting it, and telephonic instruments incircuit therewith, substantially as described.

18. In an instrument containing", selenium as a portion of an electriccircuit, two or more fitrips of conducting material separated byinulating material, 'arrangedto leave a portion of the space between'thesaid strips unoccupiedthereby, and selenium placedin the said unoccupiedspace to complete an electric circuit betwe'ezrthe saidconducting-strips, substan tially as'and for the purpose described.

' I In testimony whereof I have signed my name to thisspecification inthe presence of two subscribing witnesses.

ALEXANDER GRAHAM BELL.

Witnesses:

J os.' P. LIVEBMORE,

ARTHUR- REYNOLDS:

